This research focuses on three major goals. One aspect of the proposed studies is the continued development of genetic tools useful in the analysis of susceptibility to cancer and other diseases. The AKXD set of recombinant inbred strains derived from the cross of high lymphoma AKR/J strain and the low lymphoma DBA/2J strain have been developed, characterized with respect to lymphoma and leukemia susceptibility, and typed for numerous genetic markers. Genetic markers on Chromosomes 4 and 5 have been implicated as contributing to tumor susceptibility. By typing additional markers in this set of RI strains, we will attempt to identify additional loci that determine tumor latency and tumor type (T-cell or B- cell lymphoma). A second major effort has been the development of the MEV (multiple ecotropic virus) linkage testing stock. The purpose of this stock is to provide multiple easily typed genetic markers that can be followed in crosses with other strains, facilitating the mapping of new mutations and strain differences such as cancer susceptibility. This stock has been selected for multiple copies of the endogenous ecotropic murine leukemia virus genome widely dispersed markers in the mouse genome. These proviruses can be individually scored in a single Southern blot. The best current stock sweeps about 68% of the genome in a linkage cross. Novel proviruses are acquired in the stock by a process of germline infection and 50 of these have been propagated to fixation as potential new markers. Thirty of these have been mapped and ten are candidates for incorporation into an ultimate linkage testing stock. Three of the proviral insertions are associated with recessive phenotypes of unusual biomedical interest. One of these insertional mutations is associated with male sterility. The provirus and flanking DNA sequences have been cloned and are being analyzed as part of this program. A flanking genomic fragment detects a testis-specific transcript. We propose to identify and characterize the disrupted gene by cDNA cloning and sequencing and to investigate the mechanism by which the provirus inhibits gene expression. This mutation may provide a useful model for the further analysis of the complex process of spermatogenesis and lead to a better understanding of cases of human infertility.